2) After 19 hours, turn the dough out onto a lightly floured work surface. Punch down the dough and turn it over onto itself a couple of times. Cover with a tea towel and allow to rest for 15 minutes. After 15 minutes, shape dough into a ball. Coat hands with flour if needed to prevent sticking. Sprinkle the tea towel with half of the polenta and lay the dough on top of it, with the seam side down. Sprinkle the top of the dough with the other half of the polenta and cover with the towel. Allow to rise for another 2 to 3 hours or until dough has doubled in size.
3) To bake in the oven: While the dough is rising the second time, preheat the oven to 220°C / gas mark 8. Place a 4 to 5-litre Dutch oven in the oven while it preheats. Once the dough is ready, carefully transfer it to the preheated Dutch oven. Cover and bake for 30 minutes. Remove the lid and bake another 15 minutes or until the bread reaches an internal temperature of 98-100°C. Transfer the bread to a cooling rack and allow to cool at least 15 minutes before serving.
4) To bake on outdoor coals: Heat charcoal in a chimney starter until ash covers all of the coals. Place 20 to 24 coals on a Dutch oven table. Place a cooling rack, or other wire rack, that is at least 5cm high, directly over the coals. Set a 5-litre Dutch oven on top of this rack and allow to preheat during the last 30 minutes of the second rise. Carefully transfer the dough to the Dutch oven and cover with the lid. Place 20 coals on top. Bake for 45 minutes or until the bread reaches an internal temperature of 98-100°C. Transfer the bread to a cooling rack and allow to cool at least 15 minutes before serving.